It sounds like you have properly covered yourself.

The seller had owned the property long enough to have either had to replace them or for them to have been relatively new when they bought the house.

****************************************************************How does 0% interest for 12-18 months sound?

If they would not deal with you if you disclosed exactly what your intentions are, so you omit parts to make it sound more appealing to the seller, its unethical.

Small cottage, 598 sqft, getting it for $63,500 (was listed at $72,500) with seller replacing the whole A/C system (compressor, condenser, air handler, furnace, heat pump) and him paying all my closing cost.

Could anyone provide some insight for the future on the approximate cost to replace an apartment building stack (3 story) in its entirety?  

Replace and pay through the nose.If water came in due to foundation problems, Repair and pay through the nose.

I’m curious why you are deciding to go after such a large project on what sounds to be your first flip?

It sounds like your investments are going well.

Regular landscaping/yard care (mowing, edging, trimming, fertilizer, weed control) will be provided by ____(check one)____ [   ] Landlord  [   ]  Tenant .For all Tenants:a.Tenant agrees to keep yards, walkways, patios and decks clear and to keep premises free of junk and debris.b.Tenant accepts liability for all landscape damage and/or replacement of such, if caused by neglect, abuse or lack of water.c.Tenant may plant the beds adjacent to their dwelling to their liking, but only with those plants that are of appropriate size and type for the beds.All plants brought or caused to be brought to the property by Tenant will be cared for by Tenant.d.Tenant agrees not to cut or prune trees, hedges and shrubs.This will be Landlord’s responsibility.e.Tenant agrees to properly dispose of all plant debris and agrees to not leave such on the property.f.Landlord will consider special Tenant requests for planting and removal of plants, shrubbery and trees, but reserves the right to determine the make-up of the landscaping.g.Tenant agrees not to grow marijuana on the premises, indoors or outdoors.For Tenants of single family homes only: a.Tenant agrees to mow, water, and keep the grass, lawn, flowers and shrubbery thereon in good order and condition, applying fertilizers and weed retardant as needed. b.If Tenant fails to keep the landscaping in good order and to follow these guidelines, Landlord reserves the right to hire a landscaping service at Tenant’s expense (after a 10-day notice to perform covenant).c.Landlord reserves the right to restore the landscaping to its initial condition, as it was at the time Tenant began occupancy, or if improved during Tenant’s occupancy, to the level of such improvement.